Thermoluminescent dosimetry, commonly referred to as TLD, is a technique for radiation dose measurement. A thermoluminescent (TL) material after having been exposed to an incident flux of charged particles, such as beta rays, or uncharged particles, such as neutrons, or electromagnetic energy, such as gamma rays and x-rays, will emit light when heated. When the emitted light is measured as function of the temperature of the material over time, a glow curve is produced. The glow curve can be analyzed to determine the quantity of radiation to which the TL material had been exposed.
TLD systems have been developed for monitoring the exposure of personnel who work in the vicinity of radioactive materials, x-ray equipment, etc. Each person being monitored is given a badge to wear so that the badge will be exposed to the same type and dosage of radiation as is the person wearing the badge. Although different types of badges have been used, one commonly used badge consists of an outer holder that houses a TLD card insert usually containing two, three or four TL elements. The TLD card includes two aluminum plates that are secured together and have aligned holes forming respective windows for the TL elements. Sandwiched between the plates are two sheets of transparent Teflon polytetrafluoroethylene (PTFE) that encapsulate the TL elements at the windows. The TLD cards, and the holders as well, are provided with machine readable codes to enable automatic card and/or holder identification by a TLD card reader.
Periodically the TLD cards are processed through a TLD card reader to produce an exposure record for each person being monitored. In the TLD card reader, the TL elements in each card are heated and the thermoluminescence as a function of TL element temperature is measured as by using a photomultiplier tube. The photomultiplier tube response is processed electrically to provide a measurement of TL integrals and/or the glow curve. After a glow curve is determined, the TL elements typically are annealed so that they can be used again.
The individual TL elements mounted in the above or other composite dosimeters are commonly solid bodies of TL material in the form of wafers, ribbons, chips or discs. Other solid dosimeter bodies have been produced by compressing and heating a homogeneous mixture of fine-grain phosphor powder, such as LiF, and PTFE powder to a temperature above the softening temperature of PTFE (327.degree. C.) in a mold. The result is a matrix of phosphor and PTFE which may be produced in various shapes.
Another type of composite dosimeter is described by Yamamoto et al in "Construction of a Composite Thin-Element TLD Using an Optical-Heating Method", Health Physics, Volume 43, No. 3, pages 383-390, September 1982. This paper describes a thin-layer dosimeter element made up of a mono-layer of phosphor granules of about 0.09 mm diameter formed on a substrate polyimide film of 11 mg/cm.sup.2 thick with polyimide monomers as a binder. A thin carbon layer is coated onto the opposite side of the polyimide film to increase absorbency. A transparent Teflon film 22 mg/cm.sup.2 thick covers the phosphor layer with a gap of 0.5 mm to keep out dust, moisture, sweat and the like. Four dosimeter elements are mounted on a plastic plate housed in a plate holder that is carried in a hanger.
Harvey et al, in "Thin-layer Thermoluminescent Dosimeters Based on High-Temperature Self-adhesive Tape", Phys. Med. Biol., Vol. 24, No. 6, pp. 1250-1257, 1979, disclose another type of thin-layer thermoluminescent dosimeter. This dosimeter is based on a self-adhesive tape consisting of a polyimide plastic film with a silicon adhesive. Loose lithium fluoride crystals are sprinkled onto the adhesive tape and then the tape is sandwiched between glass slides under pressure and heated to 250.degree. C. in an oven for 45 minutes to embed the crystals in the adhesive layer. Discs are then cut out with a punch to form individual dosimeters.
Simons et al in U.S. Pat. No. 4,636,642 describes yet another method of making a dosimeter element and specifically a beta dosimeter element. A TLD chip is attached to a graphite block by a Kapton XP adhesive product manufactured and sold by the Du Pont Company of Wilmington, Del. The Kapton XP adhesive product is a thin polyimide film that has a coating of perfluoroalkoxy (PFA) resin on both sides to act as a high temperature adesive and allow heat sealing of the polyimide film to the graphite block and TLD chip. The graphite block is glued to a glass slide and then a Kapton XP square is placed on top of each graphite block, followed by a TLD chip on top of the Kapton XP square. Another glass slide is then placed on top of these composites and the entire assembly is put in a covered petri dish and baked in a 400.degree. C. oven for five minutes. After from the oven the top glass slide is immediately pressed down hard and held for one minute to compress the composite dosimeters. According to the '642 patent, the dosimeters can be annealed at 350.degree. C. in covered petri dishes for ten minutes to remove residual thermoluminescence from previous radiation exposure.